A Transparent to Dark Non‐Complementary Electrochromic Device Based on Al³⁺ Guest Ions with TMTU/TMFDS²⁺ Redox Couple for Robust Stability

Abstract Al³⁺‐based electrochromic devices (ECDs) are expected to substitute Li⁺‐based ECDs as the next‐generation smart windows options. Compared to Li⁺, Al³⁺ possess large quantities in the earth and safety, while the smaller ionic radius and three‐electron redox mechanism can break the capacity bottleneck of inorganic electrochromic materials (ECM). However, limited by the strong electrostatic interaction between Al³⁺ with ECM and the lack of matching counter electrodes, the research on Al³⁺ is still focused on three‐electrode system without applications in ECDs. Different from conventional complementary structure, the ECM/redox/CCE (catalytic counter electrode) structure is introduced to enhance the kinetics (from 1.56 × 10⁻¹¹ to 9.45 × 10⁻¹¹ cm² s⁻¹) of the Al³⁺ intercalation/extraction process. Based on this structure, Al³⁺‐based ECDs achieve a series of excellent properties: a) almost total absorption of visible and near‐infrared waveband (T_{500–1500 nm} ≈0%) under −1.0 V; b) ultra‐low driving voltage (53% transmittance modulation under −0.1 V); c) excellent memory effect with the presence of redox couple; d) wide range of color modulation capability (yellow, green, blue, and black); e) outstanding energy efficiency. Moreover, the possibility of Na⁺ as an alternative to Li⁺ is also verified and Na⁺‐based ECDs exhibit comparable electrochromic properties to Li⁺‐based ECDs.